1. Field of the Invention
The invention relates to a cylindrical reinforced plastic manhole structure and more particularly to such a structure, the body portion at least of which is made up of a plurality of nestable, curved segments.
2. Description of the Prior Art
While not necessarily so limited, the structure of the present invention finds particular utility as a manhole structure for a sanitary sewer system, a storm sewer system, for underground utilities or for industrial uses and the like.
Heretofor, prior art workers have devised numerous types of manhole, vault or catch basin structures. Tile has frequently been used as shown in U.S. Pat. No. 575,553. Corrugated metal has also been commonly used for such underground structures. Examples of this are shown in U.S. Pats. Nos. 1,265,767 and 3,390,225. U.S. Pat. No. 1,712,510 teaches a manhole casing made of inner and outer sheet metal liners with a binder material located therebetween. Manhole-like structures have often been constructed of brick, concrete block or pre-cast concrete elements as is shown in U.S. Pat. Nos. 871,977 and 3,363,876.
More recently, prior art workers have become interested in preformed manhole structures made of reinforced plastic. U.S. Pat. No. 3,938,285, for example, teaches a preformed manhole comprising a dome section integrally joined to one end of a tubular body formed on an endlessly advancing mandrel. While such structures perform well, they are bulky, difficult to handle and expensive to ship from the place of manufacture to the use site. Furthermore, such preformed structures lack versatility with respect to their ability to be properly sized in height and the like to meet the needs of a particular site.
The present invention is directed to a reinforced plastic manhole structure, the cylindrical body of which is made up of a plurality of cast or molded curved segments which may be stacked and nested for purposes of shipment. The manhole structure of the present invention may be preassembled at a nearby plant, or it may be assembled at the site, in or out of the excavation prepared to receive it. The segments are light in weight and easily handled. Nevertheless, they are so constructed as to provide excellent ring stiffness and ring compression strength so that the completed manhole structure is capable of withstanding drag-down, live-load and ring compression. All of the segments may be identical to provide building block adjustability and the segments may be readily cut in the field to adjust the height of the structure. Alternatively, the segments may be made in various heights to achieve the desired final height of the completed manhole structure, all of the segments in a given tier thereof being of the same height. The segments may be easily cut to make appropriate openings for the receipt of conduit or pipe line adaptors. The final structure is leak proof and corrosion resistant. A cast or molded reinforced plastic base may be provided for the structure, or the structure may be used with a concrete base or the like. The upper end of the body of the manhole structure is provided with a transition element adapted to support a conventional manhole cover and frame assembly. The transition element may be dome-like and cast or molded of reinforced plastic material. The transition element may be an integral one-piece structure or segmented, as described hereinafter. The transition element may also take the form of a cast, reinforced, concrete slab-like element.